1. Field of the Invention
The present invention relates to an image capture apparatus which enables high-speed focus detection irrespective of the position of the exit pupil of a photographing lens.
2. Description of the Related Art
As a general camera focus detection/adjustment method of using light beams having passed through a photographing lens, there are a contrast detection method and phase-difference detection method. As compared with the phase-difference detection method, it is generally difficult to increase the processing speed with the contrast detection method as an evaluation value is obtained while moving the focus position of the photographing lens by an infinitesimal amount, and a focus position with a maximum evaluation value is determined as an in-focus position. On the other hand, since the phase-difference detection method performs focus detection using two light beams having passed through different areas of the exit pupil of the photographing lens, it can detect a focus point without moving the focus position, thereby allowing high-speed processing. In the phase-difference detection method, however, if the symmetry of the two light beams is disturbed, the accuracy of focus detection significantly decreases.
For example, Japanese Patent Laid-Open No. 2010-113162 discloses an apparatus of performing focus detection by the phase-difference detection method using a two-dimensional sensor in which a microlens is formed in each pixel of an image sensor which receives a light beam having passed through a photographing lens. In Japanese Patent Laid-Open No. 2010-113162, manufacturing errors of the optical photoelectric conversion unit and microlens of the image sensor are considered as factors in disturbing the symmetry of two light beams used for phase-difference detection. The manufacturing errors increase the degree of vignetting by the lens frame of the photographing lens especially at the periphery of a frame, thereby increasing a difference in amount of light between the two light beams. In this example, a manufacturing error of the image sensor shifts, on the exit pupil of the photographing lens, the position of a light beam used for focus detection, thereby decreasing the accuracy of focus detection.
On the other hand, the accuracy of focus detection may also decrease when the position of the exit pupil of the photographing lens moves. Examples of a photographing lens for which the position of the exit pupil moves are a photographing lens including an optical system which can be shifted or tilted with respect to an imaging plane, and a photographing lens including an optical system part of which can be shifted for the anti-vibration purpose. To prevent a decrease in focus detection accuracy when the position of the exit pupil of such a photographing lens moves, Japanese Patent Laid-Open No. 2011-125055 proposes a technique of switching between the phase-difference detection method and the contrast detection method according to the shift or tilt amount of the photographing lens, and using it.
In the above-described technique disclosed in Japanese Patent Laid-Open No. 2011-125055, however, if the movement amount of the position of the exit pupil of the photographing lens is large, focus adjustment is performed by the contrast detection method, thereby disabling high-speed focus adjustment.